This invention relates generally to integrating spheres and, more particularly, to an integrating sphere with multiple ports for concurrently receiving light directly reflected from a sample under test.
The use of integrating spheres for the optical measurement geometry in reflectance colorimetry is a standard practice, and is described in the Commission Internationale De L""Eclairage (CIE) Publication Number 15.2 (Colorimetry), 1986, the disclosure of which is incorporated by reference herein. An integrating sphere is an apparatus with an interior cavity (typically spherical) having a highly reflective, optically diffuse white surface. The simplest integrating sphere design contains two apertures, one which admits light and another which serves as a measurement port where the amount of light on the surface of the sphere can be measured. An integrating sphere has the property that at any point on the inner surface of the sphere the illumination is essentially independent of the direction and location of the incident beam as well as the size of the beam; the inner surface is uniformly illuminated throughout, except at the point of direct illumination. Integrating spheres are used in colorimetry for the precise determination of color for a sample under test.
A common practice in colorimetry is to measure a sample with the specular component of reflection (mirror-like reflection from the surface) either included (SCI mode) or excluded (SCE mode). Other aspects of measurement may include selection of the size of the measured sample surface, spectral content of the illumination, and angle of receiver beam with respect to the sample normal. Instruments designed for colorimetry traditionally measure the sample one configuration at a time (e.g. SCI or SCE mode with a single size of measured area), usually requiring a change of configuration or another instrument to select another mode combination. For example, most integrating-sphere calorimeters are capable of measuring the sample with the specular component either included or excluded. Changing between SCI and SCE modes is usually achieved by the use of a movable segment of the integrating sphere which removes the specular component for SCE measurements or includes the specular component for SCI measurements. In such an instrument, the included/excluded option requires separate measurements with a time between to move the segment and mechanical means to do so.
Many instruments are capable of selecting the size of the area of the sample surface to be measured. Size selection is usually done with a xe2x80x9czoomxe2x80x9d optical system or movable lenses/apertures. In such instruments, changing the size of the measurement area requires separate measurements with a time between to move the lens and mechanical means to do so.
Many instruments use a second optical path as a reference measurement to normalize/compensate for changes in the illumination. Such common practice is generally referred to as xe2x80x9cdual beamxe2x80x9d optics. For the purposes of the discussion herein, such a reference path is not considered a xe2x80x9cmeasurementxe2x80x9d path, and is not part of the xe2x80x9cmulti-channelxe2x80x9d principle.
There are some colorimetry instruments with multiple measurement paths currently available. One known example measures the sample SCI and SCE simultaneously with two measurement paths. The instrument is described in U.S. Pat. No. 5,369,481 (xe2x80x9cthe ""481 patentxe2x80x9d), the disclosure of which is incorporated by reference herein. The primary path measures the sample in SCI mode at multiple wavelengths. The secondary path measures the sample in SCE mode at one wavelength, and the remaining wavelengths are calculated based on the SCI value at the common wavelength and theoretical knowledge of the wavelength dependence of the specular reflection of the sample. The ""481 patent constrains the simultaneous SCE and SCI paths (presumably measuring the same sample area-of-view size) to being xe2x80x9coppositexe2x80x9d each other relative to the sample axis normal, and describes only this arrangement of an SCI and SCE port, the number of measurement paths limited to just these two plus the conventional reference path.
Other instruments are equipped with multiple measuring xe2x80x9cpathsxe2x80x9d which measure the color of the sample in one measurement path and measure a different parameter of the sample""s appearance, such as gloss, with a second measurement system. An example includes the Color and Appearance Technology, Inc. SPECTRO/plus(copyright) Spectrophotometer, the disclosure of the product brochure for which is incorporated by reference herein. The instrument provides a separate measurement system for the gloss; this separate measurement path does not measure the xe2x80x9ccolorxe2x80x9d of the sample and has a unique geometry specific to gloss measurement standards, such as ASTM D523, published by the American Society for Testing and Materials (ASTM) of Philadelphia, Pa., the disclosure of which is also incorporated by reference herein. Therefore, the SPECTRO/plus(copyright) only has one color measurement path.
There remains a need, therefore, for further improvements in integrating spheres, and particularly, for an integrating sphere which is capable of measuring multiple parameters, such as various specular component modes and/or areas-of-view per specular component mode, without the need for succesive measurements and/or reconfiguration.
The present invention overcomes the above, and other, limitations of the prior art and the background art by providing an integrating sphere having multiple receivers capable of concurrently receiving optical radiation scattered/reflected from a diffusely illuminated sample surface, with the capability of multiple measurement modes (e.g., multiple SCE, SCE and SCI, multiple SCI), multiple areas-of-view for a given measurement mode, multiple viewing angles per measurement mode, and combinations thereof.
In accordance with an aspect of the present invention, there is provided an integrating sphere, which comprises a housing member having a cavity with an optically diffuse and highly reflective inner surface, the housing member including a sample port where a sample is placed. An optical radiation source provides optical radiation directed toward the inner surface to diffusely illuminate the sample port. A first port is disposed in the housing member and directed toward the sample port along a first line extending at a first angle relative to a first normal to the sample at the intersection of the first line and the sample surface to receive optical radiation scattered from the sample. A second port is disposed in the housing member and directed toward the sample port along a second line extending at a second angle relative to a second normal to the sample at the intersection of the second line and the sample surface to receive optical radiation scattered from the sample concurrently with the reception by the first receiver of optical radiation scattered from the sample surface. Each each of the first and second ports either is (i) an SCI port which receives optical radiation, including a specular component, reflected from the sample port along the corresponding first or second line, or is (ii) an SCE port which receives optical radiation reflected from the sample port exclusive of specular component, the first port and the second port respectively selected from the group consisting of: an SCI port and an SCE port located in non-opposite relationship to each other; a first SCE port and a second SCE port located in opposite relationship to each other; a first SCE port and a second SCE port located in non-opposite relationship to each other; and a first SCI port and a second SCI port located in non-opposite relationship to each other.
In accordance with another aspect of the present invention, the first and second ports are not limited to being either non-opposite each other or opposite each other, and the first and the second port may be respectively selected from the group consisting of: an SCI port and an SCE port located in non-opposite relationship to each other; an SCI port and an SCE port azimuthally displaced by an angle not equal to about pi radians, the SCI port located opposite to said SCE port; an SCI port and an SCE port azimuthally displaced by an angle equal to about pi radians, the SCI port located opposite to said SCE port, said first angle not equal to said second angle; an SCI port and an SCE port azimuthally displaced by an angle equal to about pi radians, the SCI port located opposite to said SCE port, said SCI port and said SCE port viewing respective non-overlapping regions of said sample; a first SCE port and a second SCE port located opposite to said first SCE port; a first SCE port and a second SCE port located in non-opposite relationship to each other; and a first SCI port and a second SCI port located in non-opposite relationship to each other.
In accordance with an aspect of the present invention, multiple measurement paths (i.e., receivers) are used to provide multiple areas of view and specular component included/excluded modes using an integrating sphere-based reflectance colorimeter/spectrophotometer for the measurement of color and appearance. Measurement paths are provided by the fitting of multiple optical receivers to a common integrating sphere, each with its respective viewing port (aperture) in the integrating sphere, and preferably with central axes converging to a common point at the sample (specimen) port of the integrating sphere. Preferably, the measurement paths are at a common angle from the normal to the sample plane (often 8xc2x0 for colorimetry) at the sample port; the paths can be displaced around the azimuth of the sample-normal axis to separate them, or the receiver paths may be coaxial, or a combination of both. The integrating sphere may be illuminated by a white light source introduced through an additional input port, or, alternatively, the light source may be substantially internal to the integrating sphere. The integrating sphere is used in a conventional way to diffuse the light to provide uniform illumination of the sample. The receiver optics collect the light reflected from the sample at predetermined angles from normal and conduct the light to preferably parallel detection means, such as multiple spectrometers or a single spectrometer having multichannel capability.